Application of cytokinins to flowers to increase pod set in Lupinus angustifolius L

Abstract

Exogenous application of a 2 mol m-3 buffered solution of N6 benzylaminopurine (BAP) to flowers on the main stem inflorescence of Lupinus angustifolius L, cv. Danja profoundly altered reproductive development by reducing post-anthesis abscission of flowers and small pods. The same effect of BAP was recorded for a mutant (abs-) of cv. Danja, in which organ abscission was completely absent, indicating that localized application of cytokinin enhanced reproductive development rather than reduced pedicel abscission per se in the parent line. Application to pedicel and sepals at the open flower stage completely eliminated flower abortion on the main inflorescence, compared with less than 50% pod initiation on untreated inflorescences, more than doubled final pod yield on the main inflorescence and increased the number of mature pods on the whole plant by 33%. A single dose of BAP, to an inflorescence which bore flowers ranging in their stage of development from post-anthesis to immature flower buds, significantly increased the number of pods initiated and at final harvest, measured on a per plant basis. A number of synthetic and naturally occurring cytokinins, including zeatin riboside and dihydrozeatin riboside, were also effective. BAP application induced a longer period of flowering and resulted in a considerably thickened raceme. This was most marked at the distal end which showed enhanced cambial development and secondary vascularization compared with untreated controls. The positive effects of BAP application on pod initiation were not restricted to cv. Danja but were found also for cv. Warrah and cv. Gungurru, both of which have enhanced pod set compared with Danja. Enhanced pod initiation on the main inflorescence generally reduced the number of pods developing on branch inflorescences. Additional application of BAP to flowers on branches, even at the most opportune time and at the most effective site, did not enhance pod initiation and, in some cases, significantly reduced pod set on these branches. The data indicate that it would be very difficult to exploit the positive effect of exogenous cytokinin application on pod set in field crops of lupin. However, selection or genetic engineering of plants with higher levels of endogenous cytokinins in flowers or flower parts at anthesis may provide a means by which to assess the importance of this factor in determining yield stability.

Consequences of transforming narrow leafed lupin (Lupinus angustifolius [L.]) with an ipt gene under control of a flower-specific promoter

“…In tobacco, TP12 is most strongly expressed just prior to, and coinciding with, full flower opening and pollen release (Drews et al 1992). The earlier study (Atkins and Pigeaire 1993) indicated that in NLL this period would be an ideal time to increase CK levels in flowers.…”

“…The rationale for this study derived from the fact that external application of CK to floral tissues of NLL at or around anthesis resulted in significantly increased pod set (Atkins and Pigeaire 1993). Because using external application of CK to the right tissue at the right time in the field is not feasible, a transgenic approach in which the phenotype would be increased CK levels in flowers at anthesis was suggested as a means to enhance pod set.…”

“…Application of benzylaminopurine (BAP) or naturally occurring cytokinins (CK) to the basal tissues of flowers at or within a few days of anthesis prevents abortion and results in greatly enhanced pod set under glass house cultural conditions (Atkins and Pigeaire 1993). Spray applications of CK in the field do not enhance podset (Dyer et al 1987); flowers on the inflorescences anthese progressively and so multiple applications, literally to coincide with anthesis over many weeks and specifically targeted to the base of anthesing flowers, would be necessary.…”

“…Spray applications of CK in the field do not enhance podset (Dyer et al 1987); flowers on the inflorescences anthese progressively and so multiple applications, literally to coincide with anthesis over many weeks and specifically targeted to the base of anthesing flowers, would be necessary. An alternative would be to increase CK synthesis in lupins by using a transgenic approach that specifically targets developing flowers at or close to anthesis (Atkins and Pigeaire 1993).…”

Effects of water stress on male gametophyte development in plants

“…Cytokinins influence a variety of developmental processes, and water stress can affect cytokinin levels in plants (Aspinall 1980;Davies et al 1986;Davies and Zhang 1991). Application of cytokinins can prevent heatinduced kernel abortion in maize and improve flower production and fruit set in other species (Carlson et al 1987;Atkins and Pigeaire 1993;Mosjidis et al 1993;Cheikh and Jones 1994). Pressurizing the roots of waterstressed wheat plants prevents browning of apical spikelets, a potential symptom of increased cytokinin level, and improves fertility (Westgate et al 1996).…”